1. Field of the Invention
The present invention relates to a cognitive radio system. More particularly, the present invention relates to an apparatus and method for transmitting reliable Coexistence Beacon Protocol (CBP) in the cognitive radio system.
2. Description of the Related Art
In recent years, with the expansion of the wireless communication system market, the shortage of frequency resources has become a concern. To address this concern, research on Cognitive Radio (CR) technology is actively in progress. In order to prevent interference in a licensed band of an Incumbent User (IU) while enabling a new CR user to communicate, the CR technology is designed to perform a transmission channel setup process of periodically or randomly measuring an IU and unexpected interference of a corresponding channel and repeating a positive communication channel setup/switching/transmission/release. For this, the CR essentially requires an IU protection function, a self coexistence function, etc. In other words, in a CR system, it is required to share an available channel set between cells and thus, it is required to share IU information between adjacent cells to avoid mutual interference. The mutual exchange of channel usage information is essential to effective system maintenance.
At present, in order to address the issue of mutual coexistence based on a radio link, the Institute of Electrical and Electronics Engineering (IEEE) 802.22 standard working group has designed for the exchange of information between a Base Station (BS) and a Customer Premises Equipment (CPE), which is terminal equipment, using a kind of Media Access Control (MAC) control message that is called Coexistence Beacon Protocol (CBP).
The BS exchanges necessary information with all CPEs belonging to a corresponding BS or a neighboring BS, using the CBP. For example, if a specific CPE being at a cell boundary receives CBP from a BS of an adjacent cell, the CPE reports the received CBP information to its serving BS. Upon receiving the CBP, the serving BS performs a resource optimization process of channel switching, transmit power control, resource renting or clustering, etc. based on the CBP information, thereby reducing interference and achieving efficient bandwidth usage.
In detail, in the conventional art, the CBP is transmitted by a BS or CPE within a cell during a Self Co-existence Window (SCW) duration (i.e., a preset time slot duration). During the SCW duration, a CPE in an active mode transmits the CBP and a CPE in a passive mode receives the CBP.
However, when a CPE that is at a cell boundary transmits received CBP to a BS, the BS may not operate in a passive mode. That is, when the CPE transmits the CBP to the BS, the BS may be transmitting CBP to the CPE. If the BS to which the CPE is to transmit the CBP is in an active mode rather than a passive mode, the BS fails to receive the CBP or a CBP collision occurs.
As described above, the conventional art has a problem that a CPE being at a cell boundary fails to support reliable CBP transmission in a cognitive radio communication system. Accordingly, there is a need for apparatus and method for transmitting a reliable Coexistence Beacon Protocol (CBP) packet in a cognitive radio system.